The need for effective and reliable backup and archive of user data information is well known. Considerable information system (IS) resources are devoted to providing backup and archive of information resident in computers and servers within any organization that produces and/or relies upon digital information.
The term “backup” means that periodically, such as each day, a backup record is made which mirrors then-present information content of computer active memory embodied as semiconductor random access memory, and/or a hard disk drive or drives, of a computer or computer server. This backup operation usually, although not necessarily, involves a transfer to magnetic tape and occurs during a period of likely minimum usage of the underlying data storage resource, such as in the middle of the night. If the storage resource is thereafter lost or becomes unavailable on account of equipment failure, or for any other reason, it is then possible to use the backup record to reconstruct the state of the information in storage as of the last backup time and date.
The daily backup procedure may be followed by a weekly backup procedure, a monthly backup procedure, a quarterly backup procedure, and so forth. At any point in the backup procedure, selected backup data storage media, frequently backup tape cartridges, may be physically removed from the system and relocated to a secure storage location away from the information processing/storage center. Secured backup tape cartridges then function as archival tape cartridges. One drawback of archival tape cartridges is that once they are removed to the secure storage site, they become presently unavailable to the computing system; and, depending upon conditions such as temperature, humidity, handling and storage conditions within the storage site, the tape/cartridge may deteriorate or degrade. If later needed, the archived user digital data information on the tape media of such cartridges may turn out to be unavailable.
One procedure which is used to safeguard data integrity of data on archive tape cartridges is to remove each cartridge periodically from the secure storage site, load each cartridge into a tape drive and unspool and respool the reeled tape, by carrying out an operation known as “repacking the tape pancake”. During this tape-spooling operation, some or all of the archive data may be read out to determine whether such data remains intact and available as an archive. If the tape media is determined to be deteriorating, as measured by error correction activity for example, a replacement archive tape cartridge may be loaded and the archived data on the failing tape cartridge may then be transferred to the replacement cartridge. Then, the failing tape cartridge can then be discarded. Such procedures tend to be time consuming, labor-intensive, and evidently expensive. Repeated handling and use of a tape cartridge shortens its useful life and can directly lead to its failure as a data archive resource.
One further drawback of tape archiving methods and technology is that drive transports are being constantly improved and upgraded technologically. It has proven very difficult to provide backwards-compatibility in tape archive systems such that more recent tape drives are able to read and recover user data from older tapes using less dense data recording formats, all other considerations being the same.
One other drawback of tape archiving methods has arisen during efforts to re-use archive tapes because of less than complete erasure of overwritten data. This problem has led some users to treat tape cartridges as one-use devices, greatly adding to the expense of tape archive systems operations and management. Also, because the tape cartridge is not a sealed system, external contaminants and influences may prevent a tape transport mechanism from successfully reading an archive tape. Further, tape cartridge handling equipment including tape transports, tend to be very complicated electro-mechanical structures, with multiple tape path control loops and other interactive tape handling processes. If any one of these processes fails or degrades, the tape may be damaged or destroyed. Moreover, tapes written on one tape transport may not be readable on another tape transport because of accumulation of head-tape alignment errors.
Tape recording has evolved since its earliest beginnings over forty years ago. Large reels of open tape have given way to small compact tape cartridges that hold increasing quantities of magnetic storage tape capable of being recorded with ever-greater information density. One form of compact single reel cartridge tape is the streaming digital linear tape system marketed by the assignee of the present invention under the DLT™ brand. The DLT system includes individual tape drives, as well as tape cartridge handling equipment and libraries. Recently, it has been proposed to create a virtual tape library by using a single DLT tape device, or several such devices within a cartridge loader environment. An example of this virtual tape library is found in commonly assigned U.S. Pat. No. 6,067,481 to Saliba, entitled: “Virtual Magnetic Tape Drive Library System”. An example of a cartridge loader environment is found in commonly assigned U.S. Pat. No. 5,760,995 to Heller et al., entitled: “Multi-Drive, Multi-Magazine Mass Storage and Retrieval Unit for Tape Cartridges. The disclosures of U.S. Pat. Nos. 6,067,481 and 5,760,995 are incorporated herein by reference thereto.
Cartridge media libraries, whether tape or optical, are well known in the art, and frequently comprise “walls of cartridges” or large cylindrical cartridge bin arrangements. A so-called “picker-gripper” mechanism (robot) operating under computer control accesses a particular cartridge bin, grips the cartridge media unit present, withdraws it from the bin, translates it to a media drive unit and causes the cartridge media unit to be loaded into the drive unit in a predetermined way. One example of an optical storage and retrieval device comprising a wall of optical media cartridges is disclosed in U.S. Pat. No. 4,675,856 to Rudy et al, entitled: “Optical Storage and Retrieval Device”, the disclosure thereof being incorporated herein by reference.
Over the past forty years tape storage has been perceived to be a less expensive method for providing off-line storage than disk drives. While tape media alone may be somewhat less expensive than equivalent rotating hard disk drive storage, when a complex electromechanical tape drive is included, the comparison becomes more equivalent. As the rotating hard disk drive storage cost-per-information-unit continues to drop, the storage industry is beginning to shift its paradigm for backup, to other storage systems, such as rotating hard disk drives.
Currently, optical and low-density magnetic media (e.g.: Iomega ZIP™ drive system) are seen as alternatives to tape backup and archive. The Linear Tape Open (LTO) Consortium is offering an alternative to streaming digital linear tape (DLT).
Moreover, it has been proposed to emulate tape systems and libraries with hard disk drive arrays by using a variety of technologies known as “virtual tape”. Virtual tape makes disk drive resources appear as if they are sequentially accessed tape drives. By using disk drive subsystems as virtual tape devices, it is possible to stream backup data at very high data rates over a storage application network (SAN). Thus, for applications and computing environments requiring higher-speed backup devices and processes, for example on the order of 40 Mbytes per second or faster, virtual tape may provide the necessary data throughput.
Computer storage systems providers such as IBM, Sun Microsystems, Storage Technology Corporation, and EMC2 Corporation, offer large hard disk drive array products which may be configured as virtual tape libraries, but which do not exactly mirror or correspond to DLT tape backup/archive systems. Examples of prior art virtual tape devices and systems are found in U.S. Pat. No. 4,467,421 to White, entitled: “Virtual Storage System and Method”; U.S. Pat. No. 5,963,971 to Fosler et al., entitled: “Method and Apparatus for Handling Audit Requests of Logical Volumes in a Virtual Media Server”; U.S. Pat. No. 6,049,848 to Yates et al., entitled: “System and Method for Performing High-Speed Tape Positioning Operations”; U.S. Pat. No. 6,070,224 to LeCrone et al., entitled: “Virtual Tape System”; U.S. Pat. No. 6,098,148 to Carlson, entitled: “Storage and Access of Data Using Volume Trailer”; and, U.S. Pat. No. 6,105,037 to Kishi, entitled: “Apparatus for Performing Automated Reconcile Control in a Virtual Tape System”. The disclosures of these patents are incorporated herein by reference. These prior disclosures fail to provide any teaching or suggestion that the disk drives or disk drive arrays performing the virtual tape drive emulation can be physically removed from an active data store and relocated to a secure data archive location and then provide the archive function typically performed by removable archive tape media.
Rotating hard disk drives are known to be susceptible to, and can be damaged by, sharp shock forces incident to handling. Such forces may cause the hard ceramic head sliders to deform the relatively soft aluminum alloy disk substrate. Accordingly, while tape storage has been emulated by disk storage, rotating hard disk drives are generally more fragile than tape cartridges from a media handling perspective.
Removable hard disk drive systems are known in the prior art. One example of such a system previously offered for sale by the assignee of the present invention under the “Passport™ brand is described inter alia in U.S. Pat. No. 5,253,129 to Blackborow et al., entitled: “Removable and Transportable Hard Disk Subsystem”. That system and patent describes a hard disk drive module which was loaded into, and thereupon electrically connected with, a base housing unit, which was in turn connected electrically to a host computer via a bus structure. A hard disk drive was shock-mounted inside of a metal cartridge to provide primary resistance to shock forces. A shock-resistant carrying case provided further shock resistance to the hard disk drive cartridge and enabled the cartridge to be safely transported and stored in a secure, shock-resistant environment. The Passport product found particular acceptance within the national security field where it is necessary to lock up hard disk drives containing data embodying national secrets or classified information in safes and secure areas at night or during periods of inattention. An improvement in the original “Passport” removable hard disk technology is found in U.S. Pat. No. 5,297,067 to Blackborow et al., entitled: “Electronic Hot Connection of Disk Drive Module to Computer Peripheral Bus”. The '067 patent describes methods and apparatus enabling a standard hard disk drive unit to be “hot” connected and disconnected via a standard peripheral bus interface, such as SCSI, with an associated computing system.
An expansible fixed disk drive data storage subsystem which enables attachment of a variable number of bus-level-interface hard disk drives at a single bus level logical address location is described in U.S. Pat. No. 5,097,439 to Patriquin et al., entitled: “Expansible Fixed Disk Drive Subsystem for Computer”, the disclosure of which is incorporated herein by reference. A rotating hard disk drive array employing redundant array of individual disks (RAID) formed on hot-pluggable circuit cards is described in Statutory Invention Registration No. H1221 to Best et al., entitled: “High Speed Small Diameter Disk Storage System”, the disclosure thereof being incorporated herein by reference.
The disclosures of U.S. Pat. Nos. 5,253,129, 5,297,067, 5,097,439 and Statutory Registration H1221 fail to describe or suggest a removable multi-drive hard disk drive system for providing not only high speed backup in a real-time computing environment, but also being separately capable of being removed to a different operating environment for providing data archival storage, periodic integrity checking and reduced bandwidth retrieval without any further physical relocation or handling of the particular drives and multi-drive modules.
Therefore, a hitherto unsolved need has remained for a removable hard disk storage array capable of emulating tape library backup and archive functions in a manner overcoming limitations and drawbacks of the prior art.